1. Field of the Invention
This invention relates generally to seals for valves. More particularly, it relates to valve seal designs which permit improved sealing effectiveness under the influence of fluid pressure acting upon the valve.
2. Description of the Prior Art
Heretofore, in valves having a pivotable valve closure member which includes a segment of a sphere as a sealing surface, e.g. butterfly or ball valves, it has been common to employ valve seals of many different configurations and materials. One approach, disclosed in U.S. Pat. No. 3,734,457 to Roos, has been to provide a valve seal ring which is of lesser inside diameter of the sealing surface of the valve closure element and which is partially restrained against radial stretching by a resilient metal hoop, whereby an interference fit is achieved between the seal and the disk resulting in compression of the seal and stretching of the hoop upon closing the disk. Still another prior art approach disclosed by Helman et al. in U.S. Pat. No. 3,608,861 and by Swain Canadian Pat. No. 695,037 has been to provide a seal member retained in a valve body recess and a rigid annular projection on the downstream side of the body recess which function as a fulcrum to limit flexure under the influence of fluid pressure to improve sealing effectiveness. These seals have included polymeric or elastomeric elements, and thus have been limited to a temperature range below the breakdown temperature of the polymer or elastomer employed.
Prior art metallic seals, suitable for elevated temperatures, are disclosed in U.S. Pat. No. 3,834,663 to Donnelly, U.S. Pat. Nos. 3,077,322 and 3,153,427 to Burtis, and Swiss Pat. No. 383,104 to Swain. Such seals are characterized by resilient expansion in a radial direction upon closure of a valve disk, and may rely on the influence of pressure acting on the seal member to enhance sealing effectiveness over some or all of the range of operating pressure.
While these and other related approaches to butterfly and ball valve seal design have proven effective in some applications, nevertheless certain problems have been encountered. In particular, valves employing prior art seal configurations have not always proven effective in bidirectional service, i.e. in applications in which the higher fluid pressure may be applied to either side of the valve. Further, such seals have been, for the most part, useful only within a limited range of operating pressures.